Hello Em,
You need a long 6mm allen key, something like this:
https://www.cromwell.co.uk/shop/hand-tools/hexagon-keys/t-handled-hexagon-key-driver-6mm-x-190mm/p/KEN6016120K
If you don't, you will need a wrench or a pair of pliers to tighten the wedge nut properly.
Your Kriieger has a...